The present invention provides techniques that are useful in the manufacture of integrated circuits among other technologies. Embodiments of the present invention relate to optimizing and monitoring the performance of a silicon oxide nitridation process and providing endpoint detection for such a process.
Advances in integrated circuit technology have led to a continuing decrease in minimum feature sizes. This scaling down of integrated circuits has resulted in the use of ultra-thin gate oxide films less than 40 xc3x85 thick. At such a thickness, some semiconductor manufacturers have used a film nitridation process in order to improve, among other reasons, the gate oxide film""s resistance to boron penetration, increase the VBD (breakdown voltage) and QBD (breakdown current) of the transistor and improve the device""s resistance to radiation damage. A variety of film nitridation processes are known including thermal anneal processes, ion implantation processes and plasma, both remote and in situ, nitridation processes.
The rate and degree of nitridation in the above processes depends on many variables including temperature, plasma power (where applicable), gas flow rates and chamber pressure among others. Regardless of the type of nitridation process used, it is important to accurately control the depth of the nitridation process as well as the degree of nitridation. In the past, known nitridation processes have used timed endpoint techniques. These timed endpoint techniques have provided adequate nitridation control for some applications but improved techniques are desirable.
Optical emission spectroscopy (OES) is a commonly used technique to capture the dynamics of a plasma-assisted process. Optical emission results from excess energy released in the form of photons from excited species that decay to a lower energy level state. OES has been primarily used in the semiconductor industry to determine endpoint during etch processes, to monitor process chemistry and for plasma diagnostic purposes.
Embodiments of the present invention provide improved techniques to control a film nitridation process. The inventor discovered that the oxide nitridation process modifies properties of the nitrided film in a manner that causes OES variations when using an in situ nitridation plasma. Embodiments of the present invention measure optical emissions during the in situ plasma nitridation process and use the measured emissions to control the nitridation process including optimizing, monitoring and/or endpointing the nitridation process.
In one embodiment, the method of nitriding a silicon oxide (SiOx) film according to the present invention includes flowing a nitrogen-containing gas into a substrate processing chamber and forming a plasma from the gas. Optical emissions from the plasma are then measured while a silicon oxide film deposited over a substrate disposed in the chamber is exposed to the plasma to obtain OES data that is used to optimize, monitor and/or stop the nitriding process.
In another embodiment the OES data is compared to OES data taken from a previous substrate processing operation to determine when to stop the nitriding process. The comparison can be made using a subtraction or other type of differential calculation, a band ratio, principal component or other pattern recognition techniques or statistical techniques among others.
These and other embodiments of the present invention, as well as its advantages and features are described in more detail in conjunction with the text below and attached figures.